Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $65.70   6.185%   $69.7635   $69.76   $69.75   $69.80  
  Purchase #2 $238.68   11.569%   $266.2929   $266.29   $266.30   $266.30  
  Purchase #3 $131.27   4.473%   $137.1417   $137.14   $137.15   $137.10  
  Purchase #4 $56.61   4.174%   $58.9729   $58.97   $58.95   $59.00  
  Purchase #5 $27.61   10.650%   $30.5505   $30.55   $30.55   $30.60  
  Purchase #6 $163.84   3.122%   $168.9551   $168.96   $168.95   $169.00  
  Purchase #7 $212.61   10.811%   $235.5953   $235.60   $235.60   $235.60  
  7 purchase totals = $896.32       $967.2719   $967.27   $967.25   $967.40